Conventionally, either for a normally opened contactor to remain closed state or for a normally closed contactor to remain opened state, it requires remaining energy provided externally. A bistable contactor differs from an ordinary contactor in that, a bistable contactor can operate stably in both a normally opened state and a normally closed state, moreover, it doesn't requires externally provided remaining energy to remain either of these two working states. Therefore, from the environmental protection and energy saving point of view of today, using a control method of a bistable contactor will be a future trend.
The use of a bistable contactor can save energy, but the control of a bistable contactor is more complicated than that of an ordinary contactor. The drive coil of a bistable contactor has a positive electrode and a negative electrode. By default, when applying a positive pulse of a certain width to a bistable contactor from the positive electrode to the negative electrode, the state of the bistable contactor will be changed from the opened state to the closed state (the state will not change if formerly it is already the closed state); when applying a negative pulse of a certain width to a bistable contactor from the positive electrode to the negative electrode, the state of the bistable contactor will be changed from the closed state to the opened state (the state will not change if formerly it is already the opened state). The pulse widths and pulse amplitudes required by different bistable contactors can be acquired in technical manuals from different contactor manufacturers.
As shown in FIG. 1, in current industrial applications, all of the bistable contactor drive circuits output the control signal of CON-ON or CON-OFF through a microcomputer I/O interface. Through optically coupled isolation, the control signal drives a bridge circuit, which is composed of four metal oxide semiconductor field effect transistors (MOSFETs), to obtain the positive/negative pulses to the bistable contactor coil ends. The drawbacks of this control method are: i) It needs to introduce a microcomputer, and the control circuit is complicate and of high cost. ii) The bridge circuit of MOSFETs can be easily damaged by electrostatic charges during the operation process, which leads to control failures. All these result in that bistable contactors have not yet been widely promoted and adopted.